The invention relates to production of a cellular ceramic body from an ion-exchanged crystalline material which has been separated from a synthetic mica gel in the form of flocculated particles. It is particularly concerned with a cellulating method wherein a gas is evolved within a shaped body to produce cells in the body.
U.S. Pat. No. 4,239,519 (Beall et al.) describes the formation of crystal-containing gels and the fabrication of papers, boards, fibers, films, and coatings from those gels. The process for preparing the gels contemplates three basic steps:
(1) a fully or predominantly crystalline body is formed (commonly a glass-ceramic body) containing crystals consisting essentially of a lithium and/or sodium water-swelling mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions among those and between those and other structurally-compatible species selected from the group of talc, fluortalc, fluorpolylithionite, polylithionite, phlogopite, and fluorphlogopite;
(2) the body is contacted with a polar liquid, normally water, to cause swelling and disintegration of the body accompanied with the formation of a gel; and
(3) the solid:liquid ratio of the gel is adjusted to a desired level depending upon the product to be prepared therefrom.
The Beall et al. patent further teaches that the gel thus formed may be contacted with a K.sup.+, Rb.sup.+, Cs.sup.+, NH.sub.4.sup.+, H.sub.3 O.sup.+, Ba.sup.+2, Pb.sup.+2, Sr.sup.+2, or Ca.sup.+2 -containing solution which leads to an exchange of Li.sup.+ and/or Na.sup.+ ions with the larger ions and causes flocculation of the gel. The mechanism underlying flocculation consists of electrically neutralizing the negatively-charged mica or clay particles which have been separated due to hydration and partial loss of interlayer cations into the surrounding solution. The floc settles out such that the supernatant liquid containing the lithium and/or sodium salt can be easily discarded or recovered. The floc may be thoroughly washed and homogenized before being molded to shape.
U.S. Pat. No. 4,239,519 is primarily concerned with use of glass-ceramic type materials to produce crystal-containing gels. However, earlier work, as reported by the Bureau of Mines in Bulletin 647, Fluorine Micas, pages 236-242 (1969), involved sintering and recrystallizing a batch composed of raw materials such as talc, silica, magnesia, and fluorides to produce a water-swelling fluormica that can be used in making paper.